discoverying water walking boots

If water walking boots haven't been discovered yet and underwater
hero rises to the surface when putting a pair on, discover them.

(Sinking while removing such on water already discovers them.)

src/decl.c

@@ -851,6 +851,8 @@ static const struct instance_globals_w g_init_w = {
     /* decl.c */
     0, /* warn_obj_cnt */
     0L, /* wailmsg */
+    /* do_wear.c */
+    0U,
     /* symbols.c */
     DUMMY, /* warnsyms */
     /* files.c */